Many medical treatments are accompanied by a pain sensation. The pain sensed within a skin region is generated by pain receptors in the skin. According to the Gate Theory of Afferent Inhibition described in, for example, “The Physiology Coloring Book,” W. Kapit et al, Harper Collins Publishers (1987), pages 88-89, the pressure sensed by large, fast-conducting tactile nerves, such as by rubbing the skin, limits the transmission gates in the dorsal horn, excludes access for the weaker pain signal, and therefore inhibits the pain signal transmission by pain nerves in the spinal cord.
The treatment of skin is often very painful and may necessitate the utilization of analgesic topical creams such as EMLA cream produced by AstraZeneca Inc., Canada, or even of anesthetic injections to inhibit the pain. Such pain inhibiting procedures are risky and also increase the total duration of the treatment.
In resent years, ultrasonic treatments of lesions located under the skin have been proposed and performed. By directing ultrasonic waves and the associated mechanical force in the form of vibrations at the lesions, a localized increase in temperature sufficient to treat the lesion is noticeable. This localized increase in temperature also causes a pain sensation. In one ultrasonic treatment, subcutaneous lesions are disrupted with focused ultrasonic waves which generate cavitation in the focal zone, in order to selectively destroy tissue. Examples of ultrasonic cavitation tissue disruptors are a device produced by Ultrashape Ltd., Israel for the reduction of fat and cellulite, which is described in US 2003/0083536 and US 2005/0261584, and a device for the treatment of malignant tissue under the skin produced by GE Medical Systems, USA. The ultrasonic frequency of most treatments is in the 1-10 MHz range, and the focused ultrasonic treatments are generally very painful.
Ultrasonic energy may be used for hair removal, as described in U.S. Pat. No. 6,544,259. Hair removal by means of an ultrasonic device is generally very painful.
Another disruptive treatment which is liable to cause pain is the vibration of hair at a frequency equal to, or slightly greater than, sonic frequency. Disruptive elements are adapted to induce cavitation and disrupt tissue. Cavitation can also be induced under the skin by means of an ultrasonic aspirator.
Another medical treatment that is generally painful is the subcutaneous injection of a medication by means of a needle, causing much apprehension to patients prior to the injection.
U.S. Pat. No. 6,132,392 discloses a pain relieving device for selectively applying three or more pain relieving modalities to an upper body region of a person, including acupressure and at least two other modalities selected from the group of vibration, massage, heat, traction and electric stimulation. The deficiencies of this device with respect to pain inhibition include a low pain reduction, lack of repeatability, and considerable inconvenience to the patient.
US 2002/0013602 discloses a method for reducing the pain associated with an injection or minor surgical procedure at a site on the skin of a patient by urging a skin engaging surface of a pressure member against the skin proximate the site, thereby stimulating the large diameter afferent sensory nerve fibers in the skin proximate the site and at least partially blocking pain signals from the small diameter afferent pain nerve fibers in the skin proximate the site. Some of the disadvantages of this method include the difficulty and inconvenience to apply pressure on skin which is in close proximity to bones, the inability to achieve treatment repeatability, and the difficulty to maintain a constant level of pressure on the skin. Also, while applying external pressure on a skin surface, the pressure receptors are pressed before any pressure is exerted on a deeper neuron extending from the pain receptor. Furthermore, the reactive force applied by bones underlying the pressed skin increases the skin squeezing effect, affecting the compression of blood vessels and of nerves.
It would be desirable to provide a method for alleviating pain during injections or ultrasonic treatments which is more easily carried out and has a greater repeatability than that of the prior art.
US 2004/0254599 discloses a method and apparatus for reducing the perceived pain resulting from the puncturing of skin at a puncture site by generating a sensory distraction, such as vibration, an acoustical signal or an electrical stimulation. One deficiency of this method is that the sensory distraction is generated by means of a relatively complicated mechanism or electronic device. Another deficiency is that a pain inhibiting pressure signal is simulated, and a limited number of pressure sensors, if any, are involved in the pain inhibiting process. A pain signal that is not inhibited by a compressed pressure receptor will therefore be transmitted.
Some prior art devices reduce the level of generated pain by limiting the depth of needle penetration into the skin. WO 2004/004803 discloses an intradermal delivery device comprising a housing including a base deeming a needle aperture, and a skin-engaging surface extending about a periphery of the needle aperture. A syringe of the intradermal delivery device includes a syringe body coupled to the housing and a plunger slidably received within the syringe body. A needle is coupled in fluid communication with the syringe body, and is movable through the needle aperture to penetrate the skin and inject a substance contained within the syringe body therein. A vacuum chamber of the intradermal delivery device is coupled in fluid communication with the base for drawing a vacuum within the base and, in turn, releasably securing the skin-engaging surface to the skin and forming a substantially planar needle penetration region on the skin. The intradermal delivery device further includes at least one stop surface fixed relative to at least a portion of the skin-engaging surface to define a predetermined distance therebetween, and adapted to cooperate with the needle to limit an insertion of the needle into the needle penetration region of the skin. Such a device is incapable of reducing pain when the medical treatment requires a deeper injection depth. Also a downward force is applied to the skin surface.
JP 2001-212231 discloses a device capable of reducing the sensed pain at the time of penetration of a syringe needle. As the housing portion of the device is pressed onto the epidermis of a patient, the air within a variable volume chamber is released. When the syringe needle is introduced into the skin through a suitable aperture of the device, the force applied onto the epidermis as a result of the pressure differential between atmospheric air and that of the chamber helps to disperse the sensed pain during penetration of the syringe needle into the skin. Only the walls of the variable volume chamber having a very small projected surface area contact the drawn skin, and therefore the pain reduction that may be realized with this device is very limited. Also, the vacuum level that is generated by downwardly pressing the housing portion onto the epidermis is very low, and is not sufficient to reduce the sensed pain to a significant extent.
JP 2005-087520 discloses a liquid medicine injector that causes a reduced sensation of pain as a skin region is punctured. A plurality of hollow needles communicate with a liquid medicine container and project outwardly therefrom. A leaf spring provides the driving force for percutaneously injecting the liquid medicine via a needle, and a suction port sucks the air in a recessed part of the container, from which the needles project. In order to reduce pain, a dedicated injector that is compatible with the configuration of the apparatus must be employed. Also, the Gate Theory of Afferent Inhibition is not mentioned in this publication, and therefore a threshold size and threshold vacuum level for achieving pain reduction is not suggested. Furthermore, the sole purpose of generating the vacuum is not to reduce pain, but also to prevent the needle from coming off from the skin in order to ensure precise penetration into the skin at a desired location and depth.
It is an object of the present invention to provide a method and apparatus for inhibiting the resulting pain which is usually sensed during a skin-related medical treatment, such as an ultrasonic treatment of the skin or during an injection into the skin, without use of an analgesic topical cream or anesthetic injection.
It is an object of the present invention to provide a method and apparatus for achieving a large level of pain reduction during a skin-related medical treatment.
It is an additional object of the present invention to provide a method and apparatus for increasing the level of pain reduction during a skin-related medical treatment with respect to prior art vacuum-assisted pain inhibiting apparatus.
It is an additional object of the present invention to provide a method and apparatus for performing painless skin-related medical treatments of high repeatability.
It is yet an additional object of the present invention to provide apparatus having a threshold size and generating a threshold vacuum level, in order to achieve a desired level of pain reduction.
It is yet an additional object of the present invention to provide apparatus that is suitable for inhibiting the transmission of pain signals in the dorsal horn by generating pressure signals in a sufficiently high number of pressure receptors in the skin.
It is yet an additional object of the present invention to provide a method and apparatus for performing painless injections with any commercially available injector.